The Pitfalls of Virtual Tape Library Sprawl

Friday Dec 28th 2007 by Drew Robb

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Gresham claims its Clareti VTL overcomes many of the complexity, performance and scalability limitations of other virtual tape offerings.

To keep up with rapid data growth and performance needs, enterprises have deployed appliances en masse and used them to create countless virtual tape libraries (VTL). The result? The backup window is being met, but management headaches are cropping up.

Instead of being the panacea to solve backup speed and management challenges, 'VTL sprawl' is causing its own share of grief.

"The problems associated with 'VTL sprawl' are the same problems IT managers have faced for a long time: managing a disparate collection of devices and processes that make up the enterprise storage environment," said Ed Ahl, North American vice president of sales and marketing for Gresham Enterprise Storage. "Performance is one aspect of the situation; i.e., more data in less time to the backup devices. This shrinks the backup window and enlarges the restore window."

He believes that Gresham offers the highest performance per pipe of any product in the enterprise storage marketplace. Single stream writes via a 4Gbps FC pipe top 250 MB per second. For a single-node Gresham Clareti VTL with four inbound pipes, this can sustain write performance at over 1,300 MB per second, or more than 4.5 TB/hour, he said.

"If the customer's initiators can send data faster, Clareti VTL can accommodate them," said Ahl. "It was designed from the beginning as an extremely high bandwidth, large capacity system."

Another situation with traditional approaches to VTL is that they sometimes have difficulty allowing data to reach real tape. This can result in lengthy periods of manual intervention. Gresham's Clareti VTL offers unattended operation straight through to the real tape without the need for intervention.

Ahl also highlighted the importance of providing meaningful and coherent information about each and every device and media attached to any VTL system.

Clareti VTL tracks and displays all relevant information about attached tape drives, changers (libraries), and media (tapes of any media type). It can discover tapes that haven't been mounted in some period of time, or the number of mounts for a given media barcode, as well as the data transfer rates to and from any virtual or physical device. All data is tracked and contained in a SQL database that allows customer database mining tools or scripts to be employed.

Gresham's product can scale in both processing and storage nodes independently. A single node Clareti VTL, for example, can manage more than 2PB of data using tape resources. Most other VTL technology, said Ahl, reaches limits of either performance or capacity. Additional VTLs are then introduced, which adds management complexity.

In addition, Clareti VTL can consolidate multiple heterogeneous virtual tape library systems from other vendors under one management interface. If a company has an installed base of 12 VTLs, for example, each one can be connected to a Clareti VTL back end, where it will be managed and operated via the internal media manager.

"The customer can now see what is happening at each of those libraries; he/she can view what virtual tapes are mounted, how long the mount time has been, what is the average mount time, what is the data transfer rate, how many virtual tapes are in each library, etc.," said Ahl. "Additionally, with Clareti VTL in the data path, back end controlled libraries and tape drives, virtual or real, can be taken offline without loss of backup/restore operations."

Clareti VTL does this by living at the SCSI layer. The back end is capable of discovering and controlling any SCSI or Fibre Channel library attached to it. All this is delivered in an appliance that includes a collection of related software processes, including kernel device drivers, memory allocators, and user-space processes developed by Gresham. No component is licensed from any other storage vendor.

The appliance runs under Linux on either AMD or Intel processors. It requires no client-side deployment, though it does use a Web-based GUI, written in PHP. This means that any Web browser can be used to operate and view Clareti VTLs. It runs its own Web server.

A recent report by the Taneja Group validates many of the claims made by Gresham. The report lays out the inherent complexity of many VTL architectures, as well as their performance and scalability barriers.

"The Gresham Clareti VTL is truly scalable, easy to manage, and reduces the complexity created within other layers of the data protection infrastructure," said Taneja Group. "Large enterprise users are often forced to ask themselves whether the bells and whistles of some VTLs are worthwhile if the VTL does not resolve tape's limited performance scalability once and for all. With Clareti VTL, it is clear that Gresham knows the problem and has a solution."